duplexultrasoundevaluationofhemodialysisaccess...

Hindawi Publishing CorporationInternational Journal of NephrologyVolume 2012, Article ID 508956, 7 pagesdoi:10.1155/2012/508956

Review Article

Duplex Ultrasound Evaluation of Hemodialysis Access:A Detailed Protocol

Victoria Teodorescu,1, 2 Susan Gustavson,2 and Harry Schanzer1

1 Division of Vascular Surgery, Mount Sinai School of Medicine, New York, NY 10029, USA2 The Zena and Michael A. Wiener Cardiovascular Institute, Mount Sinai Medical Center, New York, NY 10029, USA

Correspondence should be addressed to Victoria Teodorescu, [email protected]

Received 17 January 2012; Revised 4 April 2012; Accepted 19 June 2012

Academic Editor: Franca Anglani

Copyright © 2012 Victoria Teodorescu et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

A detailed protocol for the performance and interpretation of duplex ultrasound evaluation of hemodialysis access is described.

1. Introduction

Access is the lifeline for the hemodialysis patient, but itscreation and maintenance is a difficult undertaking. Thearteriovenous fistula (AVF) has long been recognized as thepreferred access [1, 2]. Preoperative evaluation of upperextremity veins and arteries with duplex ultrasound is auseful adjunct to physical examination, especially for thosepatients who are obese, have had multiple previous accesssurgeries or otherwise are difficult to examine well, or forthose in whom arterial or venous disease is suspected [3–5]. After creation of the access, prolonged functional patencymay prove elusive due to the development of stenotic lesionsleading to thrombosis or failure to mature. The role thatduplex ultrasound plays as part of a surveillance programis currently unclear [6, 7]. Nevertheless, duplex ultrasoundimaging lends itself well to the evaluation of hemodialysisaccess as grafts and fistulas are superficial structures. Thismodality allows identification and localization of abnormal-ities, which may potentially threaten access function andpatency. Identification and correction of access abnormalitiesat early stages may improve longevity and function as bloodflow <500/cc/min or stenosis >50% identified on duplexexam has been correlated with access thrombosis within 6months [8]. Understanding the information gained throughduplex evaluation can be difficult as the higher velocitiesand turbulent flow characteristically seen in access typicallydenote dysfunction when seen in peripheral arterial beds.

Details not normally obtained in arterial or venous studies,such as size and depth of the conduit, may be helpfulin determining whether the access is fully matured. Thispaper describes a detailed protocol for the performance andinterpretation of duplex ultrasound evaluation of hemodial-ysis access, developed through our experience in both thevascular laboratory and the operating room in the creationand maintenance of access.

2. Anatomical Facts

The upper extremities are most commonly used for dial-ysis access. An arteriovenous access (AVA) is created byconnecting a vein to and artery (AV fistula or AVF) or byinterposing a conduit, usually of synthetic material, betweenan artery and a vein (AV graft or AVG). This provides ahigh flow circuit, which may be percutaneously cannulatedfor hemodialysis access when sufficiently mature. A maturedAVF outperforms AVG, in terms of higher patency rates,freedom from infection and decrease in maintenance costs[1, 2].

AV access will typically have a thrill or vibration dueto turbulent flow within the graft or vein. Changes in thethrill may indicate a problem with the graft. A weak thrillcan denote poor arterial inflow or arterial stenosis. Feelinga pulse rather than a thrill may signify high-grade stenosisat the outflow of an AVF or at the venous anastamosisof an AVG. Furthermore, significant increase in venous

2 International Journal of Nephrology

pressure during dialysis can indicate a stenosis at the venousanastamosis or outflow vein.

3. Indications for Ultrasound Examination

Once created, an access may not function properly. Althoughsometimes physical examination may elucidate the problem,ultrasound can provide greater detail so that correction canbe planned. In the US [9], reimbursement for performingthe examination will generally be made for the followingindications:

abnormal fistula function including the following:

(i) difficult cannulation

(ii) thrombus aspiration

(iii) elevated venous pressure greater than 200 mmHg ona 300 cc/min pump

(iv) elevated recirculation time of 15% or greater

(v) low urea reduction rate of less than 60%.

clinical signs and symptoms of AV access insufficiencysuch as the following:

(i) access collapse suggesting poor arterial inflow

(ii) poorly matured fistula

(iii) loss of thrill

(iv) distal limb ischemia

(v) clinical signs of infection

(vi) perigraft mass, aneurysm, or pseudoaneurysm.

In some circumstances, a complete duplex ultrasound exam-ination may not be possible. The presence of indwellingcatheters, dressings, open wounds, or recent surgery mayphysically restrict access to scan areas. Access grafts withmultiple puncture sites may have excess scar tissue or evencalcification, which can limit imaging in some areas of thegraft. Severe edema or hematoma may reduce image reso-lution and depth penetration of ultrasound beam. Finally,contractures or other reasons for immobility may limit thepatient’s ability to be positioned properly for the best views.

4. Instrumentation

The examination is performed using an ultrasound dupleximager with pulsed wave and color flow Doppler capabilityand Doppler spectral analysis. Transducers may be curved,linear, or phased array. Curved and phased arrays are utilizedfor deeper vascular imaging such as the inflow arteries,central veins in the neck or shoulder, or in obese patients,while linear arrays are usually chosen for more superficialvascular imaging, generally the access itself. Transducerfrequencies are chosen as appropriate or necessary for theapplication and tissue depth requirements and commonlyinclude the C5-2/2.5 MHZ, L7-4/4.0 MHZ, L12-5/6.0 MHZ,P4-2/2.0 MHZ, or P4-1/2.0 MHZ. In general, high frequen-cies give better sensitivity to low flow and have better spatial

resolution, while low frequencies have better penetration andare less susceptible to aliasing at high velocities.

As with other medical information, study images, mea-surements, and data records must be archived. A digitalimage storage device capable of black and white, gray scale,and color Doppler image still frame and cine loop storage isnecessary.

Assessment of arterial steal may also require the use ofa blood pressure cuff and a photoplethysmograph (PPG)photocell. Details of this type of examination are describedelsewhere in the literature [10].

5. General Considerations

To obtain accurate results, all pulsed Doppler interroga-tion/sampling should be done at an angle of 60 degreesor less as measured between insonation beam and bloodflow direction or vessel wall. Insonation angles greater than60 degrees should never be used for any data analysis.To understand why, it is necessary to review the Dopplerequation

(FR − FT) = 2FTV cos θC

, (1)

where the Doppler frequency shift (FR − FT) is the differencebetween the transmitted frequency FT and the reflectedfrequency FR, V is velocity of the blood flow towards thetransducer, θ is the angle of insonation between the soundbeam and the direction of moving blood and C is velocity ofsound in tissue. This equation shows the direct relationshipbetween the Doppler shift and velocity and reveals why theangle of insonation is so critical to the performance of anaccurate examination.

The cosine of 90◦ is zero, so if the ultrasound beam isperpendicular to the direction of blood flow, there will beno Doppler shift. It will appear as if there is no flow in thevessel. With the ultrasound beam parallel to the direction ofblood flow at an angle of 0◦, maximum velocity would beobtained as the cosine of 0◦ is 1. However, grayscale imagequality is degraded at this angle. The angle of 60◦ is 0.5. Sincethe cosine function has a steeper curve above the angle of 60◦,errors will be magnified at angles above this measurement[11]. The following images illustrate this point (Figures 1(a)and 1(b)).

Doppler sample volume placement should be at thecenter of the vessel where the highest velocity may beobtained. Color flow Doppler imaging should be used as atool to screen for areas of high velocity and to aid in theoptimal placement of the pulsed Doppler sample volume.The pulsed Doppler sample volume should be set at thesmallest size possible to detect discrete changes in blood flowand minimize artifactual spectral broadening. Finally, thegain must be appropriately set. In a study looking at thesource of human error in determining accurate peak systolicvelocities in examinations performed by registered vasculartechnologists in accredited laboratories, incorrect Dopplerangle, sample volume placement and Doppler gain were themost significant sources of error and variability [12].

International Journal of Nephrology 3

(a)

(b)

Figure 1: (a) The angle of insonation, noted by the phrase “SVAngle” in the upper left hand corner, has been set at 42◦. Thepeak systolic velocity (PSV), the highest point at the top of thewaveform, is nearly 80 cm/sec. (b) The same vessel is examinednow at an angle of 70◦. Marking the highest and lowest pointsalong the waveforms instructs the machine to calculate PSV andthe end diastolic velocity (EDV), shown in the lower left handcorner. Using this incorrect angle, the PSV has more than doubledto 175.9 cm/sec. Great care must be taken to avoid this error asPSV is widely used as a diagnostic measure. An improper angle ofinsonation may thus result in a false impression of stenosis wherenone actually exists.

Most of the study will be carried out in a longitudinalplane, which allows for greater accuracy in Doppler angle tovessel wall estimation. This view also allows for an overallgreater appreciation of flow as seen in color flow Dopplerimaging. The transverse plane is helpful in giving an overallappreciation of the anatomy and its orientation.

Stenoses may occur at either the afferent or efferentanastomosis site, puncture sites or anywhere along the lengthof the access. Doppler spectral evaluation will alert the ultra-sonographer to the presence of a stenosis as characteristicwaveforms will be appreciated proximal to the area, at thestenosis where the highest velocities are found and distalwhere poststenotic turbulence is visualized (Figure 2).

Performance of an accurate study is more easily accom-plished when the type of access and its anatomy are knownprior to the examination.

6. Procedure

The patient should lie supine and may be semireclined withthe arm to be examined rotated externally and extended from

Figure 2: A high-grade stenosis is noted just distal to the take-off of a branch, where a marked elevation in both peak systolic(843.0 cm/sec) and end diastolic (626.3 cm/sec) velocities is found.Doppler color flow imaging demonstrates post-stenotic turbulencedistal to the narrowest segment of the vein.

the body to about a 45-degree angle. If the graft is a leg loop,the patient should externally rotate the leg to be examined.

Begin the scan of the graft or fistula with evaluation of theinflow artery in the transverse view. Scan the entire length ofthe access in this orientation all the way to the outflow veinfor an overall appreciation of anatomy.

Now the access can be more closely examined. Returnto the inflow artery and rotate the view to longitudinal.Examine the native artery proximal to the access anastamosisby pulsed Doppler, measuring the peak systolic velocity(PSV) and end-diastolic velocity (EDV) (Figure 3). Imagethe proximal anastomosis, documenting pulsed Dopplerwaveforms and PSV. As the dialysis access provides low-resistance outflow to the arterial bed, expect to see spectralbroadening and diastolic flow throughout this area instead ofthe triphasic waveforms normally seen in peripheral arterialbeds. Continue scanning the remainder of the access inlongitudinal view using color flow Doppler imaging as aguide for placement of the pulsed Doppler sample volume.

Document representative duplex images at predeter-mined locations along the course of the fistula or graft asfollows:

(i) inflow artery proximal to the fistula or graft

(ii) inflow artery distal to the fistula or graft

(iii) anastomotic sites (fistula has one site, graft has twosites)

(iv) puncture sites

(v) proximal, mid, and distal outflow vein or graft

(vi) axillary and subclavian veins.

Document waveforms and PSV in any area where velocityincrease or turbulence is noted. PSV should also be recordedin the segments proximal and distal to areas of increasedvelocity or turbulence. Care must be taken to walk the samplevolume throughout the anastomotic sites. (Figures 4, 5, and6).


Figure 3: The radial artery just proximal to a Brescia-Ciminofistula demonstrates spectral broadening and diastolic flow seencharacteristically in arterial beds with low resistance outflow inaddition to elevation of both PSV and EDV. In the absenceof dialysis access, a normal radial artery will exhibit triphasicwaveforms with no spectral broadening and PSV >40 cm/sec.

Figure 4: Normal arterio-venous fistula demonstrating markedspectral broadening and elevated velocities. The cephalic vein inthis image is relatively superficial, sitting about a centimeter or lessbelow the surface of the skin as denoted by the scale to the right ofthe color-flow image.

Figure 5: Marked turbulence and a velocity shift at the confluenceof the subclavian and innominate veins indicates the presence ofoutflow stenosis.

Figure 6: This brachiocephalic fistula has thrombosed. Waveformsdemonstrate a to-and-from characteristic indicative of a vessel withno outflow. Low PSV, the absence of color flow throughout theaccess, and the presence of echogenic material within the fistula areother findings compatible with access thrombosis.

Figure 7: Ultrasound findings indicate this recently created trans-posed basilic fistula is maturing well. The scale to the right of theimage confirms that a 5-cm length is superficial enough for easycannulation, lying 0.5 cm or less from the surface of the skin. Thediameter measures 0.73 cm. With PSV of 189.9 cm/sec and EDV of123.9 cm/sec, a volume-flow of 1792 mL/min has been calculatedby a software package incorporated into the ultrasound equipment.These details are shown in the upper left hand corner.

Document representative B-mode images of the access,including anastamosis. Measure the depth of the body ofthe access from the skin surface. If only a segment ofvein appears superficial enough for cannulation (0.6 cmor less from the surface of the skin), scan this segmentlongitudinally to provide a measurement of accessible fistula.Ideally, the superficial segment will be at least 10 cm long.For AVF, measure the diameter at representative proximal,mid and distal areas, including any aneurysms. Diametermeasurements will be necessary to calculate flow volumes[13] (Figure 7).

Diameter measurements and calculation of flow volumesmay be helpful in determining whether a newly createdfistula is sufficiently mature. Robbins et al. demonstrated thatfindings of a minimal diameter of 0.4 cm or greater alongwith blood flow rates of 500 cc/min or higher on ultrasound


Table 1

Classification Velocity (cm/sec) Image characteristics

Normal

Mid graft PSV > 150 cm/secNo visible narrowing

Distended outflow veins

Anastamosis PSV > 300 cm/sec, chaotic, disorganized flowAneurysms, puncture sites, perigraft

fluid may be visible

Moderate stenosisRatio of PSV at stenosis to PSV at 2 cm Decrease in lumen diameter

beyond anastamosis if normal-appearing <3Echogenic narrowing

Wall abnormalities

Severe stenosis

Marked velocity acceleration at stenotic areaIntraluminal echogenicity < 2 mm

lumen >50% diameter reduction

Ratio of PSV at stenosis to PSV at 2 cm Marked reduction in lumen

beyond anastamosis if normal-appearing >3 diameter with color doppler

Inflow Stenosis

Peak systolic velocities will increase at the site of Intraluminal echogenicity

stenosis with monophasic and diminished

< 2 mm lumen at velocity accelerationwaveforms distal

Flow acceleration with graft compression at

outflow anastamosis

Outflow stenosis

Mid graft PSV < 100 cm/s Intraluminal echogenicity

Distal vein > 300 cm/sec < 2 mm lumen velocity acceleration

Velocity at the proximal anastamosis will diminish Prominent collateral veins around outflow

in proportion to severity of venous outflow stenosis

Occlusion No doppler signalIntraluminal echogenicity

Graft walls appear collapsed

Occluded vein may not be visible

100

90

80

70

60

50

40

30

20

10

0Vein diam <0.4 Vein diam ≥0.4

Fist

ula

ade

quac

y (%

) P = 0.002

Flow vol <500

Flow vol ≥500

Figure 8

examination was associated with maturity in nearly 90% ofthe fistulas with those characteristics [14] (Figure 8).

7. Documentation

Still frame images and cine loop segments, if obtained,should be archived digitally with appropriate labeling as tothe patient’s identity and anatomy displayed. The specificnumber and type of images will be determined by findingsbut minimally should be sufficient in number to adequatelydocument those segments as noted above.

8. Diagnostic Criteria

Normal flow in a dialysis access graft is disorganizedwith PSV remaining fairly consistent throughout the graft.Finding pulsatile flow similar to that seen in an artery witha high resistance vascular bed or low PSV may portendimpending access failure.

The diagnosis of stenosis may be made by the followingfindings on duplex evaluation (as per Sandra L. King LVNRVT Noninvasive Laboratory, Oakland, CA, USA, ATLDuplex Protocols) (see Table 1):

(1) abnormal findings also include hematoma, pseudoa-neurysm, aneurysm and perigraft fluid (Figure 9).

(2) A “steal” is present if PVR waveforms and/or digitpressures augment significantly during graft/fistulacompression.


Figure 9: This ultrasound demonstrates a pseudoaneurysm (PSA),denoted by the white arrow, arising from the posterior wall of anaccess graft, presumably as a consequence of through-and-throughpuncture. Color Doppler shows the classic swirling “yin-yang”pattern of blood flow typically seen in PSAs.

(3) pitfalls: well-collateralized occlusion, low systemicpressure, poor Doppler angle, central venous steno-sis, or occlusion. Note: The degree of stenosis is NOTabsolute in predicting access failure.

(4) potential sources of discrepancy:

(a) Spectral data does not correlate with B-modeimage. Focal velocity >300 cm/s with no appar-ent lumen diameter reduction. Consider per-forming a correlative study under these circum-stances.

(b) Absent velocity acceleration in the presence oflumen diameter reduction by B-mode may beattributed to inflow disease or low systemicpressure.

(c) Low peak velocity measurements may be at-tributed to immature fistula.

Alternatively some labs use a doubling in the PSV to indicatea stenosis within the arterial inflow or venous outflow vessels.A PSV ratio greater than 3 when the absolute PSV is greaterthan 400 cm/sec at the anastamosis indicates a stenosis at thislevel [15].

9. Reporting

The rendering physician should review all data and recordhis or her impressions within 24 hours upon completion ofthe exam to create a final report.

Technically inadequate studies should be reported assuch to the referring physician with documentation ofthe study’s technical limitations. A typical report form isaddended (see Figure S1 in Supplementary Material availableonline at doi:10.1155/2012/508956).

10. Conclusions

Although duplex ultrasound imaging lends itself well to theevaluation and monitoring of hemodialysis access, under-standing the information gained through duplex evaluationcan be difficult as the higher velocities and turbulent flowcharacteristically seen in access typically denote dysfunctionwhen seen in arterial beds. Further details, not usuallyobtained in standard arterial and venous studies, may benecessary in order to determine whether the access isfunctional, not just patent. A detailed protocol for the per-formance and interpretation of duplex ultrasound evaluationof hemodialysis access, developed through our experience inboth the vascular laboratory and the operating room in thecreation and maintenance of access, has been described.

References

[1] NKF-DOQI, “NKF-DOQI clinical practice guidelines forvascular access,” American Journal of Kidney Diseases, vol. 30,no. 4, supplement, pp. S150–S191, 1997.

[2] KDOQI, “Clinical practice guidelines for vascular access,”American Journal of Kidney Diseases, vol. 48, supplement 1, pp.S176–S247, 2006.

[3] M. B. Silva Jr., R. W. Hobson II, P. J. Pappas et al., “Astrategy for increasing use of autogenous hemodialysis accessprocedures: impact of preoperative noninvasive evaluation,”Journal of Vascular Surgery, vol. 27, no. 2, pp. 302–308, 1998.

[4] M. Ferring, J. Henderson, A. Wilmink, and S. Smith, “Vascularultrasound for the pre-operative evaluation prior to arteri-ovenous fistula formation for haemodialysis: review of theevidence,” Nephrology Dialysis Transplantation, vol. 23, no. 6,pp. 1809–1815, 2008.

[5] M. Ferring, M. Claridge, S. A. Smith, and T. Wilmink, “Rou-tine preoperative vascular ultrasound improves patency anduse of arteriovenous fistulas for hemodialysis: a randomizedtrial,” Clinical Journal of the American Society of Nephrology,vol. 5, no. 12, pp. 2236–2244, 2010.

[6] L. Kumbar and J. Karim, “Besarab; Surveillance and monitor-ing of dialysis access,” International Journal of Nephrology, vol.2012, Article ID 649735, 9 pages, 2012.

[7] W. D. Paulson, L. Moist, and C. E. Lok, “Vascular accesssurveillance: an ongoing controversy,” Kidney International,vol. 81, no. 2, pp. 132–142, 2012.

[8] B. S. Strauch, R. S. O’Connell, K. L. Geoly, M. Grundlehner,Y. N. Yakub, and D. P. Tietjen, “Forecasting thrombosis ofvascular access with Doppler color flow imaging,” AmericanJournal of Kidney Diseases, vol. 19, no. 6, pp. 554–557, 1992.

[9] Centers for Medicare and Medicaid Services: Empire MedicalLocal Coverage Determination, August 2010, http://www.cms.hhs.gov/MCD/.

[10] A. Schanzer, L. L. Nguyen, C. D. Owens, and H. Schanzer,“Use of digital pressure measurements for the diagnosis of AVaccess-induced hand ischemia,” Vascular Medicine, vol. 11, no.4, pp. 227–231, 2006.

[11] T. Kohler and B. Mraz, Strandness’s Duplex Scanning in Vascu-lar Disorders, Lippincott Williams & Wilkins, Philadelphia, Pa,USA, 4th edition, 2010.

[12] E. Y. L. Lui, A. H. Steinman, R. S. C. Cobbold, and K. W.Johnston, “Human factors as a source of error in peak Dopplervelocity measurement,” Journal of Vascular Surgery, vol. 42, no.5, pp. 972.e1–972.e10, 2005.


[13] K. Hoyt, F. A. Hester, R. L. Bell, M. E. Lockhart, and M. L.Robbin, “Accuracy of volumetric flow rate measurements: anin vitro study using modern ultrasound scanners,” Journal ofUltrasound in Medicine, vol. 28, no. 11, pp. 1511–1518, 2009.

[14] M. L. Robbin, N. E. Chamberlain, M. E. Lockhart et al.,“Hemodialysis arteriovenous fistula maturity: US evaluation,”Radiology, vol. 225, no. 1, pp. 59–64, 2002.

[15] M. A. Needham, “Pre and postoperative ultrasound assess-ment of dialysis access fistulae,” Vascular Ultrasound Today,vol. 12, pp. 57–76, 2007.

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